1. Field of the Invention
This invention relates to an armature assembly for a selectively engageable and disengageable electromagnetic coupling such as an electromagnetic clutch or brake and, in particular, to an armature assembly incorporating a counterweight for use in balancing dynamic forces generated within the coupling by a load on which the electromagnetic coupling acts.
2. Disclosure of Related Art
One conventional electromagnetic coupling for use as an electromagnetic clutch includes an armature assembly that is adapted to selectively engage a driving rotor in order to drive a load. The armature assembly includes an armature disc connected to a driven hub by a mounting plate. The armature disc is connected to the mounting plate by a plurality of leaf springs that couple the armature disc to the mounting plate for rotation in unison while allowing the armature disc to move toward and away from the driving rotor when the electromagnetic coupling is energized and deenergized.
It has been found that the above-described coupling is subject to relatively high levels of torsional vibration and acoustic noise. In order to overcome this problem, an armature assembly was developed in which the armature disc is connected to the driven hub using a resiliently flexible plastic spider. One example of such an armature assembly is set forth in U.S. Pat. No. 5,036,964, the entire disclosure of which is hereby incorporated by reference. In the disclosed armature assembly, the spider is molded integrally with the driven hub and extends radially therefrom. The armature disc is connected to the spider at a radially outer part of the spider. Upon energization of the coupling, the spider flexes at a living hinge proximate the hub to allow the armature disc to move into and out of engagement with a driving rotor. The use of the plastic spider dampens much of the torsional vibration and acoustic noise.
The addition of a resiliently flexible spider improved upon the prior art, but also posed several problems. First, it is common to add a counterweight in many electromagnetic couplings to balance out the force exerted on the components of the coupling by the load attached thereto. In an armature assembly incorporating a flexible spider, however, the addition of a counterweight can affect the spider's living hinge. Second, the spider may fail under certain operating conditions and thereby release the armature disc.
There is thus a need for an armature assembly for an electromagnetic coupling that will minimize or eliminate one or more of the above-mentioned deficiencies.